Coal miners are the unsung heroes of America's industrial strength.

To every action there is always opposed an equal reaction； or， the mutual actions of two bodies upon each other are always equal， and directed to contrary parts.

Never underestimate the power of a simple idea executed well.

幸福的秘诀是：尽量扩大你的兴趣范围，对感兴趣的人和物尽可能友善。